In the medical practices of early days, a used syringe would be thoroughly sterilized for repeated use later. Any incomplete serialization would dangerously cause a second time infection of a patient and/or any other people. To avoid such second time infection, disposable syringes are largely produced. However, large amount of discarded disposable syringes also bring us new problems of environmental pollution and safety of syringes in use. This is because no specific measures have been taken in disposing cannulas of the discarded syringes and exposed cannulas tend to easily stab nursing or cleaning personnel and result in even more infected people. To prevent discarded syringes and/or cannulas from unexpectedly stabbing and therefore undesirably injuring and infecting other people, including nursing and cleaning persons, various types of safety syringes are particularly developed, such as those disclosed in U.S. Pat. Nos. 5,562,627; 5,405,327; 5,569,203; 5,899,887; 5,395,346, etc. All of these previously disclosed syringes have specially associated hubs and barrels, so that hubs and cannulas held thereto of used syringes can be pulled back into the barrels without the risk of unexpectedly stabbing other people.
However, all these safety syringes of prior art having retractable hub and cannula developed to improve conventional syringes have a common issue, that is, the hubs of these safety syringes must be able to be stably connected to the barrels and be pulled back into the latter after the syringes have been used, while the hubs must be connected to the barrels in an absolutely airtight manner that is very important factor in providing good quality safety syringes.
As it is known that, when the hub is tightly connected to the barrel to ensure a good airtightness at the joint of these two members, it would be difficult to pull the hub back into the barrel easily; and when the easiness of pulling the hub back into the barrel is considered, it would be inevitable to sacrifice the airtightness between the hub and the barrel.
In the conventional retractable safety syringe, the hub and the used cannula are pulled back into the barrel by engaging a forward projected conic member on the plunger with holes provided on the hub. However, experiences in using such conventional retractable safety syringe indicate that an airtight small space is formed between the hub and the plunger when the latter is about to be fully pushed into the barrel to contact with the hub. At this point, any residual medical liquid in the hub would form a resistance to the tight engagement of the hub with the engaging conic member on the plunger. A nursing personnel needs to apply an increased force to push the plunger forward to ensure the full engagement of the conic member with the hub. Such increased force would cause a vibrating syringe and discomfort the patient.
It is therefore tried by the inventor to develop an improved safety syringe to eliminate the drawbacks existing in the conventional retractable safety syringe.
A primary object of the present invention is to provide an improved safety syringe, a barrel of which has a first shoulder provided in a neck portion thereof and a hub of which has a second shoulder provided around a middle portion thereof, such that the hub is retained to the neck portion by engagement of the first and the second shoulders with each other when the hub is pushed backward into the neck portion, and that an airtight contact line is formed at joint of the two shoulders to ensure airtight connection of the hub to the barrel.
Another object of the present invention is to provide an improved safety syringe, of which the neck portion of the barrel has an inner peripheral wall gradually diametrically reduced backward and the hub has an outer peripheral wall gradually diametrically reduced backward, and the hub has an outer diameter slightly larger than an inner diameter of the neck portion of the barrel, such that the hub is stably received in the neck portion in the manner of tight fit.
A further object of the present invention is to provide an improved safety syringe, of which the hub and the neck portion of the barrel is so designed in their diameters, lengths and inclinations that a second airtight contact line is formed at a certain position within the contact surface between the hub and the neck portion.
A still further object of the present invention is to provide an improved safety syringe, a plunger of which is provided at a front end with an engaging cone having a small slit. The engaging cone is adapted to engage into two receiving holes formed on the hub of the syringe when the syringe has been fully pushed forward in the barrel. The slit on the engaging cone allows residual medical liquid in the barrel between the plunger and the hub to flow backward into the barrel to enable smooth push of the plunger fully into the barrel.